1. Field of the Invention
The present invention relates to gamma ray cameras and, more particularly, to processing gamma ray events detected by gamma ray cameras.
2. Brief Description of the Prior Art
Gamma ray cameras having radiation detectors have been utilized to form images of objects for many years. Typically, such devices are large and require specialized installations in order to function. Recently, the development of new radiation detectors has opened possibilities for the development of hand-held, portable cameras. These portable cameras, however, have difficulty in effectively transmitting data regarding detected radiation events to an external imaging system. Specifically, prior art gamma ray cameras generate both pixel address and pulse amplitude information and transmit both to the external imaging system. In applications where the radiation event rate is high, large amounts of data must be processed and transmitted. This requires either pulse processing hardware at the gamma ray camera in order to reduce the amount of data to be transmitted or the use of a very high bandwidth in order to transmit the required amount of information.
The addition of pulse processing hardware increases the complexity and power consumption of the camera, thus requiring either cooling or the use of a larger enclosure. The transmission of all data requires the use of state-of-the-art data and transmission devices and protocols, and even then places a limit on the amount of information that can be transmitted. Additionally, the use of such cameras precludes using the imaging head in a wireless mode (typically infrared transmitters) because they cannot handle the necessary data transfer rate.
One known device for processing radiation events is disclosed in U.S. Pat. No. 6,248,990. In this device, individual pixels of an image cell or array directly generate a charge in response to incident high energy radiation. Each pixel of the image cell array is coupled to an image cell circuit of a counting substrate. Each image cell circuit includes counting circuitry configured to count plural radiation hits incident on the corresponding pixel of the image cell array when a radiation hit is between a high and a low threshold value. A problem with this device is the use of a common high and low threshold value for each pixel of the image cell array regardless of the sensitivity of the pixel to incident radiation hits. Since the sensitivity of individual pixels of an image cell array can vary up to 15%, the use of fixed high and low threshold values with all of the pixels can result in the detection of radiation hits for one or more pixels that are outside the high and low threshold values for another pixel. Thus, the resulting image can include a significant amount of undesirable noise.
It is, therefore, an object of the present invention to overcome the above problems and others by providing an apparatus and method for processing gamma ray events detected by a gamma ray camera in a manner that reduces the amount of data, including noise data, that is transferred to an external imaging system for processing and conversion into an image. Still other objects will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.